By far the most significant process in carrying out a well completion in a cased well is that of providing a flow path between the production zone, also known as a formation, and the well bore. Typically, the provision of such a flow path is carried out by using a perforator, initially creating an aperture in the casing and then penetrating into the formation via a cementing layer. This process is commonly referred to as a perforation. Typically, the perforator will take the form of a shaped charge. In the following, any reference to a perforator, unless otherwise qualified, should be taken to mean a shaped charge perforator.
A shaped charge is an energetic device made up of a housing within which is placed a liner, typically a metallic liner. The liner provides one internal surface of a void, the remaining surfaces being provided by the housing. The void is filled with an explosive which, when detonated, causes the liner material to collapse and be ejected from the casing in the form of a high velocity jet of material. This jet impacts upon the well casing creating an aperture and the jet then continues to penetrate into the formation itself, until the kinetic energy of the jet is overcome by the material in the formation. Generally, a large number of perforations are required in a particular region of the casing proximate to the formation. To this end, a so-called perforation gun is deployed into the casing by wireline, coiled tubing or any other technique known to those skilled in the art. The gun is effectively a carrier for a plurality of perforators, which perforators may be of the same or differing output.